CODEWITHSUNDEEP
swiftgenerics
Twitter khuong291
Twitter khuong291

Reputation: 11700

Swift Generic issue

I am following this Generic tutorial from Apple https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Generics.html.

But in the end of tutorial. I got some problem with this:

var myStack = Stack<String>()
myStack.push("a")
myStack.push("b")
myStack.push("c")

var arrayOfStrings = ["a", "b", "c"]

if allItemsMatch(myStack, arrayOfStrings) {
    print("All items match.")
} else {
    print("Not all items match.")
}

at the line if allItemsMatch(myStack, arrayOfStrings), it says:

Cannot invoke 'allItemsMatch' with an argument list of type '(Stack< String>, [String])'

Here is my code:

import UIKit

struct Stack<Element> {
    var items = [Element]()
    mutating func push(item: Element) {
        items.append(item)
    }
    mutating func pop() -> Element {
        return items.removeLast()
    }
}

extension Stack {
    var topItem: Element? {
        return items.isEmpty ? nil : items[items.count - 1]
    }
    mutating func append(item: Element) {
        self.push(item)
    }
    var count: Int {
        return items.count
    }
    subscript(i: Int) -> Element {
        return items[i]
    }
}


func findIndex<T: Equatable>(array: [T], _ valueToFind: T) -> Int? {
    for (index, value) in array.enumerate() {
        if value == valueToFind {
            return index
        }
    }
    return nil
}

let doubleIndex = findIndex([3.14159, 0.1, 0.25], 9.3)
let stringIndex = findIndex(["Mike", "Malcolm", "Andrea"], "Andrea")

protocol Container {
    associatedtype ItemType
    mutating func append(item: ItemType)
    var count: Int { get }
    subscript(i: Int) -> ItemType { get }
}

extension Array: Container {}

func allItemsMatch< C1: Container, C2: Container where C1.ItemType == C2.ItemType, C1.ItemType: Equatable> (someContainer: C1, _ anotherContainer: C2) -> Bool {
    if someContainer.count != anotherContainer.count {
        return false
    }
    for i in 0..<someContainer.count {
        if someContainer[i] != anotherContainer[i] {
            return false
        }
    }
    return true

}

var myStack = Stack<String>()
myStack.push("a")
myStack.push("b")
myStack.push("c")

var arrayOfStrings = ["a", "b", "c"]

if allItemsMatch(myStack, arrayOfStrings) {
    print("All items match.")
} else {
    print("Not all items match.")
}

Am I missing somewhere?

Upvotes: 2

Views: 73

Answers (1)

Hamish
Hamish

Reputation: 80951

You never explicitly conform your Stack<Element> struct to your Container protocol. Therefore Swift's strict type safety will prevent you from passing it into a parameter that expects something that conforms to the Container protocol (even if it implicitly conforms).

You can explicitly conform your Stack to Container via an extension. For example:

extension Stack:Container {}

Upvotes: 2

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